I want to run 10/3 UF-B 290ft to a garage. What are the limits of load I can safely use ? air compressors etc

Answer 1

To calculate voltage drop, the formula is: Vd = 2K x L x I / Cm

Vd = Voltage Drop
K = Resistance in ohms of one circular mil foot of conductor
K = 12.9 for Copper Conductors @ 75 degrees C
K = 21.2 for Aluminum Conductors @ 75 degree C
L = One way Length of Circuit
I = Current in Conductor (Amperes) (NEC Table 310.16 - 75 degree column)
/ = Divided by
Cm = Cross Section Area of Conductor (Circular Mils) (NEC Table 8)

So, your formula would look like this:
Vd = 2 x 12.9 x 290 x 35 / 10380
Vd = 25.23 volts

According to the National Electrical Code (NEC), you are permitted a total voltage drop of 5%. This circuit results in an approximate 9% voltage drop. This is unacceptable and a NEC violation.

A good "rule of thumb" is to increase your wire or cable by one size for every 100 feet of length beyond the first 100 feet.

If you plan to operate compressors and welders and such, I recommend installing a 100 amp sub-panel.

If you have very rocky soil, install 2" PVC conduit with 3 - 1/0 THHN copper wires and 1 - # 8 copper ground wire. However, this would also require a junction/pull box approximately every one hundred feet.

If your soil is not rocky, install 2/0 Aluminum URD direct burial wire and 1 - # 6 aluminum ground wire.

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http://electricalblog.gilchrist-electric.com

Answer 2

At that distance, at 240V, a 30-amp load would result in approximately a 10 volt drop. That's adequate for most 240V units such as air compressors.

Your problem will be that you are only allowed (by code) to run one branch circuit to an outbuilding (detached garage, etc.). A multi-wire" circuit is allowed as a "single" branch circuit. If you run a 240V circuit, you'll be out of luck for 120V for lights, the radio, and the like, without relying on an expensive step-down transformer.

A better solution would be to bury #4 aluminum 4-wire srvice cable and install a 60-amp (minimum allowed) service in the garage. Then, you can run branch circuits as needed.

Answer 3

You should be able to google the answer to this question, but I think you'll be surprised by the very small load that you'll be able to run that long of a distance.

290 feet is a long run for electrical cable. There will be a lot of resistance alone outlined. To increase the load limit for a run of that distance you will need to significantly increase the wire diameter. Likely a O or OO gauge.

Answer 4

240 single phase is your best bet. that IS a long 'run', but can be overcome with higher voltages. AND it consume less energy and be cost-effective. Once in the garage, you can step it down to 120V or maintain the 240V . Always remember to consult with your local codes (information can be obtained from your city-town-village Hall). This information is free. Good luck. PS> Always try to run your compressors with higher voltages (240 single-phase) they run constantly (depending on your demands).